This invention relates to a method of and an apparatus for radiation temperature measurement for measuring the temperature of a heated object such as a steel plate or the like, the emissivity of which changes, and more particularly to a method and an apparatus for accurately measuring the surface temperature of the object by measuring both the surface temperature and the emissivity of the object, simultaneously.
More particularly, this invention relates to the following method and the apparatus for performing the method.
In a temperature measurement by radiation thermometry in an industrial furnace such as a continuous annealing furnace or the like in which a steel plate or other object is heated or in a metal at an ordinary ambient atmospheric temperature wherein the temperature is measured by detecting the radiation therefrom, several factors such as the radiant energy from the surroundings or the background noise the magnitude of which is equal to or above the radiant energy from the object to be measured and the change of the transmittance factor of the atmosphere surrounding the measuring arrangement for the radiant energy, together with the change of the emissivity of the object to be measured, will interfere with such measurement to degrade or render the conventional radiation temperature measurement impossible to carry out. These problems can effectively be solved by a radiation temperature measuring method with which this invention is more particularly concerned.
For the measurement of the surface temperature of a heated object which stands still or is moved in an industrial furnace, a radiation thermometer or radiometer capable of measuring the temperature of the object without necessitating direct contact with the object can be conveniently used. In fact, this kind of device is employed in many related fields. In a furnace, since the radiant energy coming from its wall or heat source is reflected from the object to be measured and then detected by the radiometer, such stray radiation energy becomes a great external interference or noise. This stray radiation energy must be excluded, otherwise correct temperature measurement is impossible. In addition, it is well known that when the emissivity of the object to be measured changes, the radiation thermometry measurement will generally cause a large error. The two problems as mentioned above, in effect, often make radiation temperature measurements in furnaces very erroneous. Particularly when the object to be measured is a thin or thick steel plate placed in an annealing furnace, its surface is normally oxidized while it is being heated in the furnace, accordingly the emissivity of the steel plate changes with the progression of the oxidation, thereby causing a large error in the radiation temperature measurement. This fact substantially invalidates the temperature measurement. The same situation occurs upon radiation temperature measurement of a metal having an ambient atmospheric temperature. The reason for this is that since the object to be measured (for example, metal) is at around ordinary temperatures, the radiant energy from the surface of the metal is often equal to or below the radiant energy from the surroundings.
Moreover, when the atmosphere of the measuring system absorbs radiant energy in the wavelength range which the radiometer being used can detect, and when the transmittance factor for the radiant energy is changed by a change in the concentration of the atmosphere, the radiation temperature measurement will again be subjected to large errors.